Huawei Quidway NetEngine80E Configuration Manual page 61

HUAWEI NetEngine80E/40E Router
Configuration Guide - IP Routing
Figure 1-7 Networking of L2VPN accessing the L3VPN
NodeB
NodeB
In most cases, if CSG1 needs to communicate with CSG2, CSG1 forwards data to AGG1 through
the primary PW (PW1). PW4 on AGG1 is the secondary PW, but the L3VE sub-interface is Up.
AGG1 generates and selects a network segment route because a direct route has a higher priority
than a BGP VPNv4 route learned from AGG2. However, AGG1 is not the master device of
CSG2 and does not have the Media Access Control (MAC) addresses stored on CSG2. To
forward the data, AGG1 sends an Address Resolution Protocol (ARP) request packet to CSG2.
CSG2 sends an ARP reply packet through the primary PW (PW3) because CSG2 does not
support the ARP dual sending function. The ARP reply packet reaches AGG2, instead of AGG1.
If the AGGs do not support ARP two-node hot backup, AGG2 does not back up its ARP entries
to AGG1 so that AGG1 cannot learn the MAC addresses stored on CSG2. The network segment
route from AGG1 to CSG2 becomes a black-hole route.
To address this problem, deactivate the network segment route that corresponds to the L3VE
sub-interface of the secondary PW by running the direct-route track pw-state deactive-
standby command on the L3VE sub-interface on AGG1 connecting to CSG2. When PW4 is the
secondary PW, AGG1 cannot generate the network segment route from CSG2 to its L3VE sub-
interface. In this situation, AGG1 selects the BGP VPNv4 route sent by AGG2. If CSG1 forwards
data to AGG1 through the primary PW (PW1), AGG1 forwards the data directly to AGG2.
AGG2 forwards the data to CSG2 through PW3. In this situation, no black-hole route exists.
If PW1 fails, PW2 becomes the primary PW of CSG1. If CSG1 needs to communicate with
CSG2, CSG1 forwards data to AGG2 through PW2. AGG2 then forwards the data to CSG2
through PW3. CSG2 forwards data destined for CSG1 to AGG2 through PW3. AGG2 forwards
the data to CSG1 through the primary PW (PW2). In this situation, data can be forwarded
between CSG1 and CSG2.
Issue 02 (2014-09-30)
CSG1 AGG1
PW1
PW2
PW4
PW3
CSG2 AGG2
Primary PW
Secondary PW
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1 IP Routing Basic Configuration
RSG1
BGP/MPLS IP VPN
RSG2
Data flow
ARP request packet
ARP reply packet
RNC
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